IUCCF is a two-years Marie Curie Individual Fellowship Project funded by the European Union under grant agreement 844253. The project has taken place from December 15, 2020 to December 14, 2022. The project has been coordinated by the Università degli Studi di Cassino e del Lazio Meridionale; the project principal investigator was Prof. Stefano Buzzi, while the Experienced Researched carrying out the research project was Dr. Mohamed Elwekeil. 

The project aimed to investigating beyond 5G mobile networks, and in particular the cell-free user-centric massive MIMO network concept. The project leverages the concepts of ultra-dense network deployments, cloud-based implementations of radio access networks, and cell-free network architecture. The aim is to be able to cope with the difficult challenges of beyond-5G wireless networks, which will be required to provide ultra-high data rates, to support a very large number of devices, to provide ultra-reliable and low-latency communications (URLLCs) to specific applications, and to operate with the highest levels of energy efficiency. Specifically, this project 

1. presented a novel optimization model for joint beamforming and power control in the downlink (DL) of a cell-free massive MIMO (CFmMIMO) system. The objective of the proposed optimization model is to minimize the maximum user interference while satisfying quality of service (QoS) constraints and power consumption limits. The proposed min-max optimization model is formulated as a mixed-integer nonlinear program, that is directly tractable. Numerical results show that the proposed joint beamforming and power control scheme is effective and outperforms competing schemes in terms of data rate, power consumption, and energy efficiency. 

2. employed a user-centric (UC) cell-free massive MIMO (CFmMIMO) network for providing URLLC when traditional ground users (GUs) coexist with unmanned aerial vehicles (UAVs). In this regard, we investigated power control in both the downlink and the uplink when partial zero-forcing (PZF) transmit/receive beamforming and maximum ratio transmission/combining are utilized. We consider optimization problems where the objective is to maximize either the users’ sum URLLC rate or the minimum user’s URLLC rate. The URLLC rate function is both complicated and nonconvex rendering the considered optimization problems nonconvex. Thus, we propose two approximations for the complicated URLLC rate function and employ successive convex optimization (SCO) to tackle the considered optimization problems. Specifically, we propose the SCO with iterative concave lower bound approximation (SCO-ICBA) and the SCO with iterative interference approximation (SCO-IIA). We provide extensive simulations to evaluate SCO-ICBA and SCO-IIA and compare UC CFmMIMO deployment with traditional colocated massive MIMO (COmMIMO) systems. The obtained results reveal that employing the SCO-IIA scheme to optimize the minimum user’s rate for CFmMIMO with maximum ratio transmission (MRT) precoding in the downlink, and PZF reception in the uplink can provide the best URLLC rate performances.